Lab 8.2 What is the difference in where await is called?
I'm trying to understand the difference between calling and awaiting a promisified opA(print) vs. print(null, promisified opA) - see code below (comments in the run function):
Can someone help me understand please?
const { promisify } = require('util');
const print = (err, contents) => {
if (err) console.error(err);
else console.log(contents);
};
const opA = (cb) => {
setTimeout(() => {
cb(null, 'A');
}, 500);
};
const opB = (cb) => {
setTimeout(() => {
cb(null, 'B');
}, 250);
};
const opC = (cb) => {
setTimeout(() => {
cb(null, 'C');
}, 125);
};
const promA = promisify(opA);
const promB = promisify(opB);
const promC = promisify(opC);
const run = async () => {
// This does not work, only prints 'A'
await promA(print);
await promB(print);
await promC(print);
// This works as expected
// print(null, await promA());
// print(null, await promB());
// print(null, await promC());
};
run().catch(console.error);
Answers
-
Probably, that's for a reason of internals util promisify method and how it converts callback implementation to promise-based. You can see the implementation of promisifed promA method by logging it as promA.toString() and then research further reasons of program termination. That's why after promisification it is correct to receive result from promisified function and use it then.
0 -
@akaiurin said:
Probably, that's for a reason of internals util promisify method and how it converts callback implementation to promise-based. You can see the implementation of promisifed promA method by logging it as promA.toString() and then research further reasons of program termination. That's why after promisification it is correct to receive result from promisified function and use it then.Ah, that makes sense - thanks.
0 -
duplicate, see https://forum.linuxfoundation.org/discussion/857785/lab-8-2
0
Categories
- All Categories
- 175 LFX Mentorship
- 175 LFX Mentorship: Linux Kernel
- 745 Linux Foundation IT Professional Programs
- 372 Cloud Engineer IT Professional Program
- 168 Advanced Cloud Engineer IT Professional Program
- 73 DevOps IT Professional Program - Discontinued
- 3 DevOps & GitOps IT Professional Program
- 98 Cloud Native Developer IT Professional Program
- 7.6K Training Courses & Learning Paths
- AI & ML Training
- Blockchain & Decentralized Identity Training
- Cloud & Containers Training
- Cybersecurity Training
- DevOps & Site-Reliability Training
- Linux Kernel Development Training
- Networking Training
- Open Source Best Practice Training
- System Administration Training
- System Engineering Training
- Web & Application Development Training
- 2 LFD103-JP クラス フォーラム
- 4 LFD210-CN Class Forum
- 764 LFD259 Class Forum
- 681 LFS101 Class Forum
- 2 LFS158-JP クラス フォーラム
- 162 LFS207 Class Forum
- 3 LFS207-DE-Klassenforum
- 4 LFS207-JP クラス フォーラム
- 61 LFS241 Class Forum
- 52 LFS242 Class Forum
- 42 LFS243 Class Forum
- 19 LFS244 Class Forum
- 4 LFS250-JP クラス フォーラム
- 166 LFS253 Class Forum
- 19 LFS256 Class Forum
- 1.4K LFS258 Class Forum
- 165 LFS261 Class Forum
- 26 LFS267 Class Forum
- 792 Hardware
- 202 Drivers
- 68 I/O Devices
- 37 Monitors
- 95 Multimedia
- 173 Networking
- 91 Printers & Scanners
- 87 Storage
- 768 Linux Distributions
- 81 Debian
- 67 Fedora
- 22 Linux Mint
- 13 Mageia
- 24 openSUSE
- 150 Red Hat Enterprise
- 31 Slackware
- 13 SUSE Enterprise
- 356 Ubuntu
- 465 Linux System Administration
- 31 Cloud Computing
- 73 Command Line/Scripting
- Github systems admin projects
- 98 Linux Security
- 78 Network Management
- 101 System Management
- 46 Web Management
- 105 Mobile Computing
- 18 Android
- 72 Development
- 1.2K New to Linux
- 1K Getting Started with Linux
- 392 Off Topic
- 121 Introductions
- 181 Small Talk
- 29 Study Material
- 944 Programming and Development
- 310 Kernel Development
- 616 Software Development
- 976 Software
- 368 Applications
- 182 Command Line
- 5 Compiling/Installing
- 68 Games
- 317 Installation
- Archived
- 2 LFD140 Class Forum
Upcoming Training
-
August 20, 2018
Kubernetes Administration (LFS458)
-
August 20, 2018
Linux System Administration (LFS301)
-
August 27, 2018
Open Source Virtualization (LFS462)
-
August 27, 2018
Linux Kernel Debugging and Security (LFD440)
